I was so close!
All I missed was the InsertSheet, I tried to use the SetDesignType
My code snippet:
If oProjData.AddiCDBDesign(SchName) Then
oProjData.SetiCDBDesignType SchName, VDDT_SCHEMATIC
cmprint ("Added design " & SchName)
cmprint("Failed to add design " & SchName)
Because your question was a method of the first use for me, it became study.